Base to ogive/seating depth truths

A

Al Nyhus

"It'll never work!"
'Morning from sunny South Dakota. :)

The subject of a bullets base-to-ogive measurement and how it relates to seating depth comes up from time to time. And there seems to be some confusion as to how two bullets with differering base-to-ogive dimensions can have the same seating depths. There is a belief that if a two bullets have different b-o dimensions that somehow the seating depth is off by the same amount.

To illustrate, I made two .30 cal. bullets this morning with different b-o measurements, then seated both bullets (using the same seating stem length) and measured the dimension from the base of the case to the ogive of the bullet. The dies I used are the same, the jackets are the same J4's from the same lot, the cores are identical in weight and antimony content...the only difference is that I backed the point up die out a bit to change the b-o dimension on one of these bullets. Both bullets measured .3084 on the shank and .3086 over the pressure ring.

So, like Jackie Gleason used to say: "Awaaaay we go...."

Photo #1 shows a base-to-ogive measurement of .380 on bullet 'A'
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Photo#2 shows a base-to-ogive of .400 on bullet 'B', fully .020 difference between bullets.
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Photo #3 is the .380 (bullet 'A') b-o bullet seated.
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Photo #4 is the .400 (bullet 'B') b-o bullet seated.
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Clearly, there is no difference in the true seating depth of the bullet. The distance from the back of the case to the major diameter of the bullet is identical in both examples, even with a .020 difference in the b-o meaurement of the two bullets.

So where did the .020 go? Simple. The .400 b-o bullet has .020 more shank length that the .380 b-o bullet. Or in other words,,,there is a .020 difference in how much bullet is in contact with the inside case neck. This also translates into a .020 difference in where the base of the bullet is relative to the top of the power column. If you look closely, you can see that the base of the bullet is visbly different in the case neck. This is a bit hard to see because of the angle of the camera.

But insofar as the .020 difference is bullets relates to the actual seating depth...in other words...where the 'contact point' of the bullet is relative to the rifling...there is no difference.

Thoughts and ideas welcome. :) -Al
 
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"Ogives"

Al: My results also, identical as yours. Ogive point-of-contact remains the same regardless of ogive to base, or for that matter, ogive to nose tip, length. When I point this out to someone, they usually say, " but you now have .010"/ .015", etc. less space in the case", or "ya, but neck tension will vary since there is a difference of .010"/ .015", etc. of neck contact". About as important as that bird that may have flown over the path of your bullet on its way to the target. Outstanding job & photos: a BIG thank you.:)
 
Neck tension

FB: yes, I agree with what you're saying, I believe there would be a difference on the amount of "pull" on the bullet, but I've tested side-by-side, and could find no difference on group size, out to 200 yd., with my 6BRs', 6ppc, 22BR, etc. Bullets were segregated using the Sinclair comparator: one "batch" with variations up to .025", the other identical. Loaded up with proven accuracy loads, fired side-by-side, and could not say one group was better, or worse than the other. I'm sure those with more skills than I could find a difference, but I cannot, so I do not take it into consideration.
 
Al,
Great work on discribing why different shank length gives us the same case base to ogive length. When buying hand swaged bullets from the same manufactor,that`s using the same die,the shank length will vary with each lot. I assume this is due to different lots of J-4 Jackets & Cores used,and it`s not a problem that the shank length does vary. My question is this: Did you try making up enough bullets of each lot,and then without moving the seating stem,try shooting each lot at say 200 yards,and see if there`s any difference in accuracy? Keeping each lot at the same base (of brass case) to ogive length? In other words: once you find the seating depth with a certain bullet , does the variation in shank length affect the need to find the "new" seating depth? Or do you just keep the same number/adjustment on the seating die. I know what works for me;) ,just curious as to what your practises are :confused:.Thanks Mike Kerwood, Kodiak Alaska
 
Al,

isn't this predictable if the variable that is introduced is one that affects the shank length, but leaves ogive position unchanged on the bullet?

Is there anything that can happen in the bullet making process that will change the position of the ogive on the bullet? Like, varying amounts of lube, force used to point up, etc? Thanks --Greg
 
Mike:

I've tested different 'runs' of my bullets at 200 with b-o dimensions from .365 to .400. In my test rig (30BR) I couldn't tell any difference in average group size, group location on target, observed pressure signs or chronograph data. I also did some 'mix and match' testing with Lot A @ .365, Lot B @ .400 and Lot C a combination of b-o lengths from .365 to .400. I couldn't tell any difference 'on target' from any of these lots.

I don't change the seating stem length for different bullet lots....for two reasons that may or may not be applicable to other peoples setups. I use a lot of 'jam', for one thing. And since I just make bullets for myself and one good friend, I adjust my point die to maintain as close to identical b-o dimensions from run to run as possible. I like to stay within .005 b-o from lot-to-lot (different jacket lots) and within .002 b-o difference within a particular 'run'. Most of them will run no more than 001 difference.

I'm interested in your results also, Mike.

Thanks for the nice comments and good shootin'. :) -Al
 
glp said:
isn't this predictable if the variable that is introduced is one that affects the shank length, but leaves ogive position unchanged on the bullet?

Is there anything that can happen in the bullet making process that will change the position of the ogive on the bullet? Like, varying amounts of lube, force used to point up, etc? Thanks --Greg
Click to expand...

'Morning, Greg. :)

Yes...many of those things will have a bearing on how a bullet measures. I know with my setup, once the die is up to temperature and if I don't go brain dead :mad: in how I end the stroke on the handle...things seem to measure pretty consistently.

My dies are Larry Blackmon's excellent tool steel dies so I'm more of a Slave to the Lube Gods than those using carbide. :eek:
 
Al, The long guys measure their bullets and segregate them for bearing length. The theory is keeping the ES down as much as possible. Now in short range, this is probably a mute point. One thing that may come into play is the difference in charge density in the case. Again, in short range it probably doesn't effect things enough, but some testing may be in order.

Different makers of bullets have different "shank" lengths, and I think one must adjust for seating depth for them. Since you are using the same dies for the bullets you're making, the ogive isn't changing, which the seater stem pushes on.
 
Wayne Shaw said:
Different makers of bullets have different "shank" lengths, and I think one must adjust for seating depth for them. Since you are using the same dies for the bullets you're making, the ogive isn't changing, which the seater stem pushes on.
Click to expand...

Wayne..good points as always. :)

I agree that a user should adjust for seating depth between different bullet makers. A BIB 7, a 10X 7, my 'Dakota B1's, Mike Bigelows killer 'Biggie' 7's.. may not interchange. A lot of this has to do with the leade angle and the bullet diameter.

Where the seating stem contacts the bullet opens up a whole new area....;)

Thanks, Wayne! :) -Al
 
Al & Wayne,
I agree with you two. I have to adjust the seating depth from Lot to Lot on even "Hand Swaged Bullets. Al if your able to keep tolorances that close I can see where you don`t have the need. I primarily shoot B.I.B bullets in my 30 BR & 308 Winchester. While Randy makes a very fine bullet,the difference in shank length or other variables is enough to have to adjust the seater for a new "Case Base to Ogive Length" or what I call a Comparator length, for each lot.All of our club matches are held at 200 yards.and it can make a real difference,at least to me. Both of you are know by "Reputation" as winners or at least close to it all the time. I just wanted to know if I was practising the same methods of accomplished Shooters. Although the amount of adjustment maybe small (.002"-.005") it`s enough to go from a group the size of the 10 ring,to a "Wipe Out" of 50-5X,of a small ragged hole. Thanks for taking the time to educate the rest of us, Michael Kerwood, Kodiak Alaska
 
Another part of this puzzle is what I call the 'ogive profile' on a particular bullet. My example shown in these photos show measuring the case from the back to a specific diameter at the front....which is how most shooters do it.

There is also a good case to be made for measuring the 'front profile'....referencing your measurement from where the bullet actually contacts the lands and including the throat angle. Bob Green makes what looks to be a great tool for checking bullets in this fashion. http://greensrifles.com/New_Products.html
 
Bob Green's tool works very well. It provides excellent precision and keeps OAL consistent, which is an issue regardless of what your barrel prefers.
 
If you modify the seater stem to contact the bullet farther down, closer to the bore diameter, I think you'll get more consistant results. After all, that's where the bullet contacts the rifling. The seaters I've opened up to fit farther down seems to stick a little when pulling the round out, but it's not bad.

Some seaters have a fairly shallow hole for the bullet nose to fit in, and VLD types can actually bottom out there, instead of on the ogive.
 
Al & Wayne,
Thanks for the information on the "Bob Green Tool" as it looks like it would solve some of the inconsistent lengths I get when loading cartridges,and checking them with a comaprator. The BIB bullets are very consistent,within the same lot. However when changing lots I do find the need to move the seater,anywhere from .001"-.005" with the same design bullet. It`s easy to find the right seating depth again,when I use a new lot to fireform brass. Good reason to make bigger orders of bullets,so that when I find the right length, I don`t have to hunt for the right seating depth,or Base to Ogive length. Bob Green`s tool looks like it`s worth the money. I`ll Private message Wayne, to get some seater stems opened up.That`s a great point about the seating stem contacting the point, not the bullet ogive. Thanks again for the info Guys, Michael Kerwood, Kodiak Alaska
 
Since all my .30 barrels like a lot ;) of jam, I've never spent much time measuring the foward portion of my bullets. For those barrel/bullet combos that are fussy about a specific seating depth and/or where changing the seating depth by .003 or so shows a marked changed in accuracy, a tool like Bob makes could be a lifesaver.
 
Al .............,

Very nice pictures! You're observations are correct. However, I've found that when not dealing with true benchrest grade bullets there can be "another" problem that will slip by your findings.

I have encountered brand name bullets (in the same box) that "appear" to have been made on different machines. The ogive was slightly different on some bullets ..... just enough to give a variation in the effective seating depth. When bullets are seated, they are gripped high on the ogive. However, bullets contact the rifling low on their ogive, and the difference can have quite an affect on the distance to the rifling. This sometimes results in unbelievable flyers.

I believe it's a good idea to measure loaded all rounds from the cartridge base to the lowest part of the bullet ogive. Then you'll know for sure. That will eliminate some unexplained flyers. I have an article about this on my website, in the Tech Tips section. Visit www.larrywillis.com

- Innovative
 
Larry,
Good point, I believe that as well that the seating depth should be measured from where the lead angle in the throat and the bullet engage. I have been offering caliper comparators that have the same angle as the throats; the results and feedback have been good.
 
Wayne Shaw said:
If you modify the seater stem to contact the bullet farther down, closer to the bore diameter, I think you'll get more consistant results.
Click to expand...
That can have its problems too though maybe not in centrefire applications.

I used to use a Redding Competition seating die for all my .308 loads until I buggered up the seating plunger with just a tad compressed loads behind 200 & 220 grain projectiles. It turns out that the tolerances of the Redding die were so tight that the extra force needed for the job sprung the mouth of the seating plunger recess & galled the guide tube walls. Redding replaced all the way to Australia by return post (thank you, Redding) but my guess is that a die to address lower down the ogive of big projectiles could only be at a trade off of close tolerances & precision - which is hardly what I want. I reckon the same issue would arise with any die with equivalent tolerances under the same stress, either threaded or arbour press type.

I figured out that if the projectile was seated most of the way with a conventional seater that controlled runout, then final seating to precisely locate the ogive might be possible using a rig with an oversize plunger, as long as there was some way you could locate the cartridge case - by the neck maybe.
 
I think there are a couple of chioces - - -

Peole who jam their bullets a lot don't have the problem but those who depend on a specific seating depth or want to shoot with their bullets off the lands need a reliable way to load predictably.

Perhaps a larger diameter stem migh be a solution for a stem that touches the bullet close to where it would touch the lands.The other choices are a device to measure the bullets between where the stem touches and where they will touch the lands, always JAM the bullets HARD or simply ignore the situation. We still have SOME choices until January 20. :D
 
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Here's an idea ...

Pete ..............

Using a larger diameter seating stem seems like a good idea, except you can't force the bullet down with contact on such a shallow taper. That would shave (or seriously mark) the bullet once pressure is added. I believe the solution is to use the best bullets available, and measure the bullet depth at the most effective location on the rifling.

I've made such a device that also measures headspace using a digital gauge. I'll have it available for sale in the next few weeks on my website. Visit www.larrywillis.com

- Innovative
 
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